Multipole switching mechanism

ABSTRACT

A switching mechanism for multipole operation having a base and having up to four contact-carrying modules symmetrically mounted on the base, the modules being simultaneously operable by electromagnets for use as a contactor or operable by a lever for use as a disconnect switch, the module being adapted to receive auxiliary contact blocks operated in tandem with the contacts of the main module.

United States Patent 5 6] References Cited UNITED STATES PATENTS [72] Inventors John L. Haydu Owings Mills;

m ml .8

DCM

BMlF o N d Wm AH 1] 2 22 Primary Examiner-Harold Broome AttarneyWood, l-lerron & Evans [45] Patented Oct. 19,1971 [73] Assignee Rowan Controller, lnc. Westminster, Md.

ABSTRACT: A switching mechanism for multipole operation having a base and having up to four contact-carrying modules symmetrically mounted on the base, the modules being simul- 335/132 taneously operable by electromagnets for use as a contactor or l-lOlh 50/04 operable by a lever for use as a disconnect switch, the module 335/132, being adapted to receive auxiliary contact blocks operated in tandem with the contacts of the main module.

[54] MULTIPOLE SWITCHING MECHANISM 16 Claims, 13 Drawing Figs [51] Int. [50] Field of 197, 202; 200/166 S, 153.7, 48; 337/46, 47, 48, 43

PATENTEDUCT 19 IQTI SHEET 1 GF 4 INVENTO PATENTEDDU 19 |97| SHEET U BF 4 MUL'IIPOLE SWITCHING MECHANISM This invention relates to a switch mechanism for multipole operation and more particularly, the invention relates to a modular contact structure for assembling or building up contactors, disconnects and auxiliary contacts associated therewith.

In the instant description, a contactor refers to those switching devices which have electromagnetically operated contacts, contactor: being used principally in controlling industrial equipment. Disconnect switch" refers to a manually controlled device having the same type of contacts as found in a contactor, but the disconnect switch is used upstream" of the contactor as the primary on-off control for the power to the system. Auxiliary contacts, as discussed herein, are used primarily in association with the contactor and have small contacts whose power-carrying requirement is very small compared to that of the contactors with which they are associated.

The existing practice in the manufacture of contactors and disconnect switches has been to employ completely difierent casings and other parts for twoand threeand four-pole contactors. Thus, a four-pole contactor carrying a specified current per pole would be a completely different unit from a three-pole contactor carrying the same current per pole. Further, a disconnect switch of the same power-carrying capability would employ still another completely different design from the contactor.

All of this leads to considerable expense in the manufacturing process as well as in the cost of the final product and requires a substantial inventory of diverse contactors and disconnect switches to accommodate the various requirements of industrial practices.

An objective of the present invention has been to provide a modular contact structure and a base adapted to receive up to four modules, the modules being symmetrically balanced on the base regardless of the number of them. Thus, with only two standardized parts, that is, the base and the contact module, three or four different types of contactors can be built up and by adding a disconnect base, a disconnect switch can be built up using the same main contact modules.

It has been still another objective of the invention to provide a module of the type described above which is adapted for use either in connection with a contactor having base-carrying electromagnet structure for operating the contactors or a base having a lever for operating the module contacts and functioning as a disconnect switch.

It has been another objective of the invention to provide a modular contact structure including a casing, a plunger reciprocably mounted in the casing and accessible from the two opposed edges of the casing so as to be operably engaged by an operator at one edge and to engage the plunger of an adjacent stacked module at the other edge. This concept of casing and reciprocable plunger is employed in the main contact modules of the present invention as well as in the auxiliary contact modules of the present invention.

As to the auxiliary contacts, it has been an objective of the present invention to provide a module having only two molded parts, namely a casing and plunger. The auxiliary contact module of the present invention is mountable on a main contact module to be operated by it or it can be mounted on another auxiliary contact module to be operated by it or can be mounted on certain commercially available pushbutton structures to be operated by them. Further, the auxiliary contact module of the present invention can he changed as to timing or normally closed or open condition simply by a change in the contact-carrying plunger.

As to both the main contact module and the auxiliary contact module, none of the operating elements requires a screw or rivet to hold it in place. Rather, the casing and plunger structure are configurated to receive the metallic operating elements in a nesting relationship. In the case of the auxiliary contacts when the plunger is snapped into position, all parts are held in their proper positions. As to the main contact module, when the two casing halves are joined together. all of the parts previously laid into the casing in nesting relationship are held in their proper orientation.

It has been another objective of the invention to provide, in a main contact module of the type described, a loop configuration for the movable contact which provides for an increase in the force of application of the contacts as the magnitude of the current increases, thereby minimizing the possibility of contacts exploding open under severe overload currents before a fuse can interrupt the circuit.

These and other objectives of the present invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 is a perspective view, with parts broken away illustrating an assembly of contactor base, main contact modules and auxiliary contacts.

FIG. 2 is a cross-sectional view of the assembly of FIG. 1 taken along lines 22 of FIG. 1.

FIG. 3 is a cross-sectional view of the assembly of FIG. 1 taken along lines 3-3 of FIG. 2.

FIG. 4 is a diagrammatic bottom plan view of the contact module, partly in section, illustrating the locator means by which the modules are mounted on the base.

FIG. 5 is a diagrammatic plan view of the contactor base illustrating the manner in which the modules are symmetrically mounted.

FIG. 6 is a cross-sectional view of the auxiliary contacts taken along lines 6--6 of FIG. 1.

FIG. 7 is a cross-sectional view taken along lines 7-7 of FIG. 6.

FIGS. 8 and 9 are cross-sectional views taken along lines 8-8 and 99 respectively, of FIG. 6.

FIG. 10 is a cross-sectional view similar to that of FIG. 7 illustrating the structure for changing the sequence of contact operation.

FIG. 11 is a top plan view of a disconnect switch employing the modules of the present invention.

FIG. 12 is a cross-sectional view taken along lines 12-12 of FIG. 1 1.

FIG. 13 is a cross-sectional view taken along lines 13-13 of FIG. 11 but showing the position of switching linkage reversed from that of FIG. 12.

GENERAL ORGANIZATION In FIG. 1 there is shown a contactor embodiment of the invention is indicated at 15. The contactor includes a base 16, a plurality of contact modules 17 and a stack of auxiliary contact modules 18.

The base has an operator in the form of an armature 19 which is engageable with an actuator 20 reciprocably mounted in each module 17. Each actuator 20 is engageable with a movable contact of its respective module to effect its opening and closing upon energization or deenergization of an electromagnet which operates the armature l9.

Integral with the actuator 20 is a stem portion 21 accessible from the side of the module opposite the armature I9. The actuator 20 and its integral stem 21 form a plunger within the module which is adapted to actuate the auxiliary modules 18. Each auxiliary contact module 18 also includes a plunger 22 reciprocably mounted in the casing of the module. The main contacts plunger actuator 20 effects the operation of the auxiliary contacts through direct engagement of the plunger 22.

The base 16 includes a mounting block 25 having a locator means for attaching up to four modules symmetrically with respect to the base. The symmetry is a valuable feature in that it balances the load on the armature, creating a uniform wear condition and precluding binding of the armature during operation. The locator means includes six slots 27 on one side of the base adapted to receive cooperating keys 28 on the module and square holes 29 on the opposite side of the base adapted to receive square pegs 30 (FIG. 4) integral with the opposite side of each module. Each module has two keys 28 which fall into two slots 27 and correspondingly two pegs 30 which drop into the two holes 29.

The manner in which the various numbers of modules ca be mounted on the base is illustrated in FIG. 5. While singlepole operation is not normally contemplated, it is obvious that a single module could be positioned in the number one position of the A Group of FIG. 5. Two modules can be mounted in the 2 and 3 positions of Group A or the 1 and 2 positions of Group B. For three pole operation, the modules should be mounted in the 1, 2 and 3 positions of Group A.

Four modules could be mounted in the four positions designated as Group B, it being observed that the outboard modules three and four will overhang the base slightly, with their keys and pegs being engaged in only one of the respective slots and holes.

THE BASE The major portion of the base is the molded block 25 which has two coils 35 and 36 molded integrally with it. At each side of the block 25 are U-shaped legs 37 forming a pocket 38 between them. A generally U-shaped stationary core half 39 is inserted within the pocket 38 and retained therein by a mounting plate 40 which is bolted to the legs 37 by bolts 41. A movable core half 44 overlies the stationary core half 39 and is U- shaped having legs 45 straddling adjacent portions of the windings 35 and 36. The core half 44 consists of a stack of plates 46 having side plates 47 mounted on the outside of the stack. The side plates 47 have flanges 48 projecting beyond the stack 46 and overlying a part of the stack 46, the upper surface of the flanges 48 being flush with the upper surfaces of the laminate. Compression springs 49 are mounted between the block 25 and the flange to urge the armature 50 upwardly. Pins 53 projecting from the armature are engageable with hooks 54 mounted on the block (See FIG. 2) and limit the extent of the upward movement of the armature.

The combined surfaces of the flanges 48 and the core stack 46 present a surface engageable with the actuators 20 of the modules mounted on the base.

As shown in FIGS. 1 and 2, the base has terminals 60 and 61 which are electrically connected to the cores 35 and 36 respectively. It can be observed that the cores can be connected either in series or in parallel depending upon the specific requirements of the system and thus, doubling the capability of the contactor.

At the upper end of the base are overhanging flanges 62 and 63 adapted to receive hook-shaped elements on the modules as will be described in detail below. The flange 63 contains the slots 27 and the flange 62 contains the square holes 29 by which the balanced mounting of the modules is effected.

MAIN CONTACT MODULE Referring to FIGS. 1 and 2, the main contact module 17includes a two-part casing 70 joined together by rivets 71 at opposed comers. Each casing half is internally configurated to receive the operating parts which will be described below in a nesting relation so that when the casing halves are riveted together all of the parts will be disposed in their proper positions within the casing but without requiring any screws or comparable securing means.

Contained within the casing is a generally U-shaped connector 72 having a lead wire connecting screw 73 threaded in a leg 74 of the connector which is exposed to the outside of the casing for accessibility. A pigtail 75 connects one end of the connector '72 to a movable contact 76 which projects inside the casing and lies adjacent and approximately parallel to one leg of the U-shaped connector. Thus, a loop is formed with the movable contact to create interacting flux lines which assist in maintaining the contacts closed. The free end of the movable contact 76 has a silver alloy tip 77 which is urged by a spring 80 into engagement with a similar tip 78 of a fixed contact 79. The spring 80 has one end 81 seated in a recess 82 in the casing and the other end 83 bearing against the free end of the movable contact.

The fixed contact 79 has a connector screw 84 for connecting a main lead wire to the fixed contact. Both contacts have small connector screws 85 for connecting auxiliary leads to the contacts.

Referring to FIGS. 2 and 3, each module has a plunger 20 of somewhat zigzag configuration. The plunger includes a lower leg which is engageable by the upper surface of the armature 19. The leg 90 terminates in a curved upper surface 91 which provides a shoulder engageable with a curved surface 92 on the movable contact. The plunger continues upwardly with an upper leg 93 which passes through a hole 94 in the casing and its upper end 95 is exposed for engagement with a plunger 22 on the auxiliary contact 18. The plunger 20 is disposed rather loosely in the hole so as to permit some slight sideways movement in order for it to accommodate to the pivotal movement of the movable contact 76.

The casing has at its lower end an integral hook which carries the keys 28 forming part of the locater means for the casing with respect to the base. The hook has an inclined surface 101 which mates with the corresponding surface on the flange 63. At the other side of the casing is a movable hook 102 having an inclined leg 103 which normally underlies the flange 62 and engages a similarly inclined surface on that flange. The hook has a leg 104 projecting into the casing, the leg 104 terminating at its inner end in a lug 105 engaged by one end 106 of a compression spring 107, the other end of which bears against a shoulder 108 within the casing to urge the hook into a seating engagement with the flange 62. The hook has a slot 109 which is exposed and which is adapted to receive a screwdriver tip whereby the screwdriver can be pivoted against a projecting surface 1 10 of the casin g to move the hook outwardly during the engaging and disengaging of the module with respect to the base. Thus, no screws are required to secure the module to the base.

The module contains an arc suppressor plate 111 which is U-shaped and which straddles the contact tips without contacting them. Immediately above the arc suppressor is an opening 113 through which the contacts may be viewed and their condition determined. This is the normal condition of the module when used in a disconnect as will be discussed below. However, when used as a contactor, it is normally preferred that the contacts be enclosed and in this event a plug 114 is seated in the opening 113.

AUXILIARY CONTACTS The auxiliary contact module has a generally T-shaped casing 119 which includes a mounting leg 120 projecting generally perpendicularly from a contact-carrying leg 121. The mounting leg has a hole 122 through which a mounting bolt 123 passes to secure the auxiliary contacts to each other as well as to a main contact module. The leg 120 is also recessed at 124 to receive a compression spring 125.

The leg 121 is hollow thereby providing a hole through which a plunger 126 is reciprocably mounted. As shown in FIGS. 6 and 7, the plunger has a flange 127 at its lower end. As can be seen from FIG. 7, the lower end of the casing leg 121 has an inwardly projecting shoulder 128 upon which the flange 127 normally rests and against which the flangeis urged by the compression spring 125. The plunger is positioned within the casing by forcing it against a beveled surface 129 at the lower end of the auxiliary contact so as to snap it into position. Thus, no screws are required in the assembly of the module.

An integral lug 130 projects below the flange 127 and is adapted to be received in the hole 94 in the casing of the main contact module or alternatively to pass through an opening 131 in the upper end of an adjoining auxiliary contact when the auxiliary contacts are stacked upon one another.

A pair of fixed contacts 133 are molded integrally in the casing leg 121 and have contact tips 134 projecting into the hollow leg. The contact plunger may have differing configurations depending upon the requirement of being normally open, normally closed or a requirement of sequential operation of the auxiliary contacts. In each instance, however, the plunger carries a hat-shaped auxiliary contact 136 having contact tips 137 adapted to engage the fixed contact tips 134.

For example, as shown in FIG. 7 the upper module has an upwardly facing recess 138 into which the U-shaped portion 139 of the bridging contacts seats. A compression spring 140 has one end bearing against the bridging contact and the other end surrounding a post 141 depending from a flange 142 at the upper end of the plunger. These contacts are in normally closed condition and are urged into normally closed condition in part by the compression spring 125 which urges the plunger downwardly and in part by the spring 140 which maintains a pressure on the bridging contacts.

In the lower module, the plunger has a downwardly facing recess 143 into which the U-shaped portion 139 of the hatshaped bridging contacts is seated; This positions the contact tips 137 below the fixed contact 134 and spaces them from the fixed contact so that the contacts of that module are normally open. Upward movement of the plunger will close the contacts and a compression spring 144 will maintain them closed.

Still another variant is shown in FIG. Ill. There the module is normally open but it can be seen that the plunger has a recess 146 which is slightly higher than the recess of the lower module of FIG. 7. As a consequence, while the contact tips are maintained spaced from the fixed contact tips, the spacing is closer and contacts will close earlier than the contacts of the lower module of FIG. 7.

CONTACT OR OPERATION When the requirements of the particular system are known, the contactor is built up from the main contact modules and auxiliary contact modules and a sing e base. For example, if a four-wire system is involved, a four-pole module is built up with the modules being seated on the base as shown in Group B of FIG. 5. Each module is first positioned with its keys 28 in the appropriate slots 27 and a screwdriver is applied to the slot 109 of the movable hook to slide it outwardly and to permit the module to be pivoted into that seated position in which its pegs 30 drop into their respective holes 29. The screwdriver is then released and the pressure of the spring 107 forces the hook securely against the flange 62 to maintain the main contact module in position.

The appropriate auxiliary contact modules are selected and stacked on one or more of the main contact modules with the lug 130 projecting into the hole 94 so that the plunger is engageable with the plunger 126 of the auxiliary contact module.

The terminals 60 and 61 to the coils 35 and 36 are connected in series or parallel depending upon the power supply and the contactor is ready for electrical connection to the device which it is to control. That connection is simply made by connecting the main contacts in series with the power lines to the device to be controlled.

The springs 49 hold the armature l9 and hence, all plungers in an upper position thereby maintaining the contacts open. When the electrical device is to be operated, the coils are energized to pull the armature down and to permit the spring 80 to drive the movable contact into engagement with the fixed contact 79 thereby closing the circuit.

To preclude the destruction of the module by a severe overload exploding the contacts apart, the adjacent legs of the movable contact and the connector 74 produce interacting flux lines creating a repulsive force proportional to the magnitude of the current flowing through the contacts. Hence, the greater the current the greater the force applied to hold the contacts together until a fuse blows or the fault is cleared.

DISCONNECT SWITCH As stated above, one of the advantages of the main contact module is its capability of being used to build up a disconnect switch. In that environment, an entirely different base is employed, as illustrated in FIGS. 11 to 13. It should be understood that the invention is not restricted to the specific details of the disclosed base. Rather, any base will suffice so long as it is capable of receiving the modules and effecting the simultaneous operation of their actuators 20 to open and close the module contacts when the disconnect handle is operated.

One form of base indicated at 149 is illustrated in FIGS. 11 to 13, the base having one module applied. The base includes a molded block 150 having overhanging flanges 151 and 152 adapted to receive the fixed hook and the movable hook 102 of the contact module as described above in connection with the application of the module to a contactor base. The flange 151 includes locator notches 153 which precisely positions the modules on the base for engagement by respective operators to be described below. The block includes two centrally located posts 154 and 155 between which a module may be positioned. A switch handle 156 is mounted on the posts to pivot about an axis 157. The handle is formed by two bellcrank levers each being pivoted at 157 to a respective post 154 or 155. Each bellcrank lever has an arm 159 which extends generally upwardly, the arm being interconnected by a bar 160 forming a handgrip for the switch handle. The bellcrank levers have short arms 161 to which depending links 162 are connected. Each link 162 is pivoted at its upper end at 163 to its respective arm 161. At the lower end, each link 162 is pivotally connected to an elongated rod 164 extending substantially entirely across the base 149. The rod 164 interconnects a pair of links 165 and three similar links 166 of a toggle linkage. The link pair 165 is pivoted at each side of the base on pins 167. The other links 166 are mounted adjacent each module position, each of the links carrying a wire operator 168 having a free end 169 adapted to project into a conical recess 170 in a respective actuator 20 of the module. Each link has a slot 173 at one end which receives the rod 164, the slot permitting the toggle action of the linkage. The other end of each link 166 carries a roller 174 which rides in an arcuate strap 176 fixed in the block 150. A compression spring 177 is mounted between two washers 178, the washers bearing against the rod 164 and the wire 168 respectively. The spring imparts a snap action to the toggle linkage.

The operation of the disconnect can be perceived by comparing FIGS. 12 and 13. In FIG. 12, the modules are in a contact open position. To close the contacts, the switch handle 156 is thrown clockwise as viewed in FIGS. 12 and 13, to the position of FIG. 13. The movement of the switch handle causes the arm 161 to pull the link 162 upwardly raising the bar 164 upwardly. The upward movement of the bar causes the toggle linkage to shift with a snap to the position of FIG. 13, the roller 174 riding downwardly in the strap 176. The reversal of the position of the toggle linkage brings the wire operator down and effects the closing of each set of contacts in the respective modules. Reversal of the operation will effect the opening of the contacts with a snap action as imparted by the spring 177.

We claim:

1. A switch mechanism comprising:

a base having an opening in the upper surface thereof;

a movable operator on said base, said operator having an upper surface exposed through the opening in the upper surface of said base;

a plurality of discrete contact modules each having a fixed and movable contact;

means for individually mounting each of said modules external of said base on the upper surface thereof and overlying said operator;

an actuator in each module engageable with said movable contact and engageable by said operator through said opening in the upper surface of said base whereby movement of said operator causes simultaneous movement of the movable contacts of all of said individually mounted modules through their respective actuators.

2. A switch mechanism according to claim 1, wherein:

said actuators of each of said modules are exposed at the lower surfaces of said modules for engagement by said operator and is exposed at the upper surfaces of said modules, the upper surfaces of said modules being adapted to receive and support an auxiliary contact unit; and further comprising a plurality of discrete auxiliary contact units, each individually mounted on the upper surfaces of different ones of said modules and completely and independently supported thereby, said auxiliary units having a plunger engageable and operable by said actuator; whereby said auxiliary contact units remain mounted upon and fully supported by the respective supporting module when said supporting module is removed from said base. 3. A switch mechanism according to claim 2, in which the plungers of each of said auxiliary contact units are exposed at both ends of said unit, each of the upper surfaces of said units being adapted to receive and support another auxiliary contact unit, whereby multiple units may be stacked upon each other and operated by said actuator and removable from said base while remaining fully mounted and supported by said module.

4. A switch mechanism according to claim 1, further comprising:

an electromagnet including a magnetic core portion mounted on the lower portion of said base, an annature movable mounted above said electromagnet and forming said operator, and spring means normally urging said armature away from said electromagnet. 5. A switch mechanism according to claim 1, further comprising:

a handle mounted on said base, and linkage means between said handle and said operator to effect the opening and closing of said contacts upon operation of said handle. 6. A switch mechanism according to claim 5, further comprising:

a window in each module through which said contacts can be observed. 7. A switch according to claim 1, further comprising: a pair of posts mounted on said base, a handle pivoted to said posts, an elongated bar forming said operator movably mounted on said base adjacent said actuators, and linkage means connecting said handle to said bar. 8. A switch mechanism according to claim 1, further comprising:

a window in each module through which said contacts can be observed. 9. A modular contact structure comprising: a casing; at least one contact fixed in said casing; at least one contact movable in said casing; and a plunger extending through said casing, said plunger being slidable in said casing and engageable with said movable contact to open and close said contacts; said plunger being accessible from opposite ends of said casing for engagement by an operator at one end to move said actuator and for engagement of a plunger of a contact module stacked on the other end; means at said other end of said casing adapted to grip opposed flanges projecting from the upper end of a base; said gripping means including a fixed hook at one end for receiving one said flange and a slidable hook on the other end for receiving the opposite flange; and spring means urging said slidable hook toward said fixed hook to resiliently clamp each module on said base. 10. A modular contact structure according to claim 9, said casing being a single molded element having a hole therethrough, and said plunger being a single molded element slidably mounted in said hole. 1 l. A modular contact structure according to claim 10,

further comprising:

said hole having an elongated recess,

a return spring in said recess,

said plunger having a flange engaged by said spring.

12. A modular contact structure according to claim 10,

further comprising:

a shoulder at one end of said hole,

said plunger having a flange snap-fitted past said shoulder and normally seated on said shoulder,

and a spring in said hole urging said flange against said shoulder.

13. A modular contact structure according to claim 9,

said casing comprising two internally contoured casing halves,

said casing halves securely receiving said fixed and movable contacts in nested relation, said contacts being retained in position solely by said nested relation.

14. A modular contact stmcture according to claim 13,

further comprising:

a U-shaped connector having one leg exposed through one edge of said casing for receipt of a connecting wire, and another leg projecting into said casing,

a pigtail connecting said other leg to one end of said movable contact,

said movable contact lying generally parallel and in close proximity to said other leg,

and said fixed contact projecting out the opposite edge of said casing.

15. A switch mechanism comprising:

a base;

a movable operator on said base, said operator having an exposed upper surface;

a plurality of discrete contact modules each having a fixed and a movable contact;

means for individually mounting each of said modules on said base overlying said operator;

an actuator in each module engageable with said movable contact and engageable by said operator in said base whereby movement of said operator causes simultaneous movement of all the movable contacts of all of said individually mounted modules through their respective actuators;

mating locator means on said base and modules respectively selectively permitting the symmetrical mounting of one to four modules on said base;

said locator means including a first set of locating elements on each of said discrete contact modules, and at least seven second sets of locator elements each adapted to mate with any one of said first sets of locator elements; and

said second sets of elements being carried by said base and positioned symmetrically with respect to said operator.

16. A switch mechanism comprising:

a base;

opposed flanges projecting from the upper end of said base;

a movable operator on said base, said operator having an exposed upper surface;

a plurality of contact modules each having a fixed and movable contact;

means for mounting said modules on said base overlying said operator;

each said module having a fixed hook at one end for receiving one said flange and a slidable hook on the other end for receiving the opposite flange, and spring means urging said slidable hook toward said fixed hook to resiliently clamp each module on said base; and

an actuator in each module engageable with said movable contact and engageable by said operator in said base whereby movement of said operator causes simultaneous movement of all movable contacts through their respective actuators. 

1. A switch mechanism comprising: a base having an opening in the upper surface thereof; a movable operator on said base, said operator having an upper surface exposed through the opening in the upper surface of said base; a plurality of discrete contact modules each having a fixed and movable contact; means for individually mounting each of said modules external of said base on the upper surface thereof and overlying said operator; an actuator in each module engageable with said movable contact and engageable by said operator through said opening in the upper surface of said base whereby movement of said operator causes simultaneous movement of the movable contacts of all of said individually mounted modules through their respective actuators.
 2. A switch mechanism according to claim 1, wherein: said actuators of each of said modules are exposed at the lower surfaces of said modules for engagement by said operator and is exposed at the upper surfaces of said modules, the upper surfaces of said modules being adapted to receive and support an auxiliary contact unit; and further comprising a plurality of discrete auxiliary contact units, each individually mounted on the upper surfaces of different ones of said modules and completely and independently supported thereby, said auxiliary units having a plunger engageable and operable by said actuator; whereby said auxiliary contact units remain mounted upon and fully supported by the respective supporting module when said supporting module is removed from said base.
 3. A switch mechanism according to claim 2, in which the plungers of each of said auxiliary contact units are exposed at both ends of said unit, each of the upper surfaces of said units being adapted to receive and support another auxiliary contact unit, whereby multiple units may be stacked upon each other and operated by said actuator and removable from said base while remaining fully mounted and supported by said module.
 4. A switch mechanism according to claim 1, further comprising: an electromagnet including a magnetic core portion mounted on the lower portion of said base, an armature movable mounted above said electromagnet and forming said operator, and spring means normally urging said armature away from said electromagnet.
 5. A switch mechanism according to claim 1, further comprising: a handle mounted on said base, and linkage means between said handle and said operator to effect the opening and closing of said contacts upon operation of said handle.
 6. A switch mechanism according to claim 5, further comprising: a window in each module through which said contacts can be observed.
 7. A switch according to claim 1, further comprising: a pair of posts mounted on said base, a handle pivoted to said posts, an elongated bar forming said operator movably mounted on said base adjacent said actuators, and linkage means connecting said handle to said bar.
 8. A switch mechanism according to claim 1, further comprising: a window in each module through which said contacts can be observed.
 9. A modular contact structure comprising: a casing; at least one contact fixed in said casing; at least one contact movable in said casing; and a plunger extending through said casing, said plunger being slidable in said casing and engageable with said movable contact to open and close said contacts; said plunger being accessible from opposite ends of said casing for engagement by an operator at one end to move said actuator and for engagement of a plunger of a contact module stacked on the other end; means at said other end of said casing adapted to grip opposed flanges projecting from the uPper end of a base; said gripping means including a fixed hook at one end for receiving one said flange and a slidable hook on the other end for receiving the opposite flange; and spring means urging said slidable hook toward said fixed hook to resiliently clamp each module on said base.
 10. A modular contact structure according to claim 9, said casing being a single molded element having a hole therethrough, and said plunger being a single molded element slidably mounted in said hole.
 11. A modular contact structure according to claim 10, further comprising: said hole having an elongated recess, a return spring in said recess, said plunger having a flange engaged by said spring.
 12. A modular contact structure according to claim 10, further comprising: a shoulder at one end of said hole, said plunger having a flange snap-fitted past said shoulder and normally seated on said shoulder, and a spring in said hole urging said flange against said shoulder.
 13. A modular contact structure according to claim 9, said casing comprising two internally contoured casing halves, said casing halves securely receiving said fixed and movable contacts in nested relation, said contacts being retained in position solely by said nested relation.
 14. A modular contact structure according to claim 13, further comprising: a U-shaped connector having one leg exposed through one edge of said casing for receipt of a connecting wire, and another leg projecting into said casing, a pigtail connecting said other leg to one end of said movable contact, said movable contact lying generally parallel and in close proximity to said other leg, and said fixed contact projecting out the opposite edge of said casing.
 15. A switch mechanism comprising: a base; a movable operator on said base, said operator having an exposed upper surface; a plurality of discrete contact modules each having a fixed and a movable contact; means for individually mounting each of said modules on said base overlying said operator; an actuator in each module engageable with said movable contact and engageable by said operator in said base whereby movement of said operator causes simultaneous movement of all the movable contacts of all of said individually mounted modules through their respective actuators; mating locator means on said base and modules respectively selectively permitting the symmetrical mounting of one to four modules on said base; said locator means including a first set of locating elements on each of said discrete contact modules, and at least seven second sets of locator elements each adapted to mate with any one of said first sets of locator elements; and said second sets of elements being carried by said base and positioned symmetrically with respect to said operator.
 16. A switch mechanism comprising: a base; opposed flanges projecting from the upper end of said base; a movable operator on said base, said operator having an exposed upper surface; a plurality of contact modules each having a fixed and movable contact; means for mounting said modules on said base overlying said operator; each said module having a fixed hook at one end for receiving one said flange and a slidable hook on the other end for receiving the opposite flange, and spring means urging said slidable hook toward said fixed hook to resiliently clamp each module on said base; and an actuator in each module engageable with said movable contact and engageable by said operator in said base whereby movement of said operator causes simultaneous movement of all movable contacts through their respective actuators. 